(1) Field of the Invention
The present invention refers to an improved kind of floor cleaning and sweeping machine, as well as to a filtering arrangement for an air stream being sucked in and re-circulated in the surrounding environment, mounted on and used by such machine.
(2) Description of Related Art
Floor cleaning and sweeping machines, in particular such machines intended for industrial application, which are generally used to sweep and clean very large floor surfaces subject to considerable soiling, are largely known to be based mainly on:                the creation—in a position close to the floor to be cleaned—of an almost sealed, i.e. air-tight suction or vacuuming chamber;        the suction of the air being taken into said chamber, in which there are contained the soil particles to be removed; and        a filtering process, which said air being so sucked in is due to undergo, as carried out with the aid of an appropriate filtering element, which is usually provided in the form of a filter plate or sieve of a type generally known as such in the art, duly delimited and sustained by a suitable support structure.        
Largely known in the art is also the need for said filtering element to be periodically cleaned to prevent clogging which jeopardizes the entire cleaning process and, as a result, the effectiveness thereof.
According to the prior art, owing to said filtering element being rather large in the overall size thereof and being further subject to clogging rather frequently, a replacement of the complete filter cartridge or filter plate—as this is usually done in other sectors, such as for instance in the case of air filters used in road haulage vehicles in general and in passenger motor-cars—proves practically quite expensive on the whole, in terms of both machine downtime and direct costs.
As a result, a common practice has been establishing in the specific sector, based on providing means for the same filter to be able to periodically undergo a vigorous cleaning process as brought about through a shaking action imparted to the filter, wherein said shaking occurs in particular in a rotatorily variable direction.
The above-mentioned shaking action is obtained by applying a light-weight support frame onto a face of the filter plate, and linking to said frame a rotary electric motor, whose rotor is rigidly connected with one or more weights that are sensibly eccentric relative to the axis of rotation of said rotor.
When such motor is switched on, it is allowed or caused to operate at a constant speed, so that the eccentric load placed on the rotor thereof gives of course rise to an alternating variable-direction mechanical impelling force, which is obviously transferred—via bearings or other similar or equivalent means—on to the respective stator and—from such stator—further on to said support structure and, as a result, ultimately to the entire body of the filter plate. In this way, the filter plate is therefore stressed mechanically by an alternating impelling force that acts in a rotary manner, but in all cases in planes that extend orthogonally to the main plane of the filter plate, wherein the latter is of course orthogonal to the direction of the air stream to be filtered.
As a result, said motor is therefore operated periodically—and whenever this proves necessary or may be considered appropriate—to bring about a vigorous shaking action on the filter plate and, ultimately, almost totally remove the dust and dirt particles retained by and collected onto the same filter plate, thereby restoring the operating efficiency thereof.
What has been explained above belongs to the prior art and—as such—is largely known to all those skilled in the art, so that it shall be appreciated as having been recalled here for the purpose of facilitating the reader in more readily understanding the actual scope of the present invention.
Additionally, in other sectors of industry and technique in general, the cleaning process for an air or gas filter in general is usually carried out by submitting the related filter plate to a mechanical vibrating action performed in a more or less automatic manner.
Known from the patent DE 3438575 A1 there is in fact an arrangement for periodically cleaning the lint filter of a drying machine, such as in particular a clothes drying machine, which is adapted to submit said filter to a vibratory effect of such frequency and extent as to cause the lint and the other particles that are retained by said filter to be released from the filter plate or cartridge to then collect by gravity into an appropriate container provided under said filter plate.
The vibratory effect acting on said filter element is generated by an appropriate electrically operated device that is adapted to produce a mechanical oscillation on a member thereof that is connected to said filter plate so as to be able to transmit the thus generated vibrations thereto.
Such solution, although not inherently novel, proves effective and is easily embodied. However, it has a major drawback in that the oscillations are generated at a fixed frequency, so that the actual effectiveness thereof is practically limited to those dirt particles settling onto the filter plate, which are mostly stressed, i.e. most liable to be affected by such frequency, and, therefore, in particular to those dirt particles that, as combined with the portion of filter plate which they are settled upon, have an oscillatory eigenfrequency, i.e. a natural oscillation frequency that is similar or even equal to the stressing frequency of said vibrating arrangement.
As a natural result of such circumstance, what is obtained with an arrangement as the above-described one, actually, is just a partial cleaning effect on the filter element, so that it can be most readily appreciated that, in the case of the floor-cleaning machine being used through extended periods of time, the need unavoidably arises for specific maintenance actions to be taken manually on the filter element in view of ensuring a continued efficiency thereof, i.e. a circumstance that is in all cases quite undesired in an industrial environment, where a primary goal is achieving as high as possible competitiveness levels under as great as possible a reduction in costs of any kind whatsoever.
Known from the disclosure in the patent publication DE 29620412 U1 is a clothes drying machine, which is provided with a filter plate, or cartridge, that is mechanically linked with means for generating a mechanical vibratory action, wherein the thus generated vibrations are applied in a direction extending orthogonally to the filter plate, which is in turn made in the form of a planar element arranged in a vertical position.
The solution described in the above-cited publication, although representing an improvement from the general point of view of a clothes drying machine, does however not constitute or show any substantial difference from the solution set forth in the formerly cited patent, since the filter plate is even in this case caused to vibrate, although at definite intervals, at an anyway constant frequency, so that the same practical drawbacks ultimately arise.
Cleaning the filter element by subjecting it to a periodical shaking action has generally proved effective, as well as simple to implement. However, it has been found—also on an experimental basis—that, in the case of particularly dusty environments or quite intensive uses of the filter-containing machine, cleaning the filter by solely subjecting it to an action of mechanical shaking, as this has just been explained, is by no way always sufficient, since there may have been sucked in, or taken in, particular kinds of dust that, due to the particular nature thereof, tend to cling to the filter plate in a particularly tenacious manner, so that a much more effective shaking action would be needed on the filter element, actually, to achieve adequate filter cleaning results.
In particular, known in the industrial floor-cleaning sector is a number of solutions that are generally based on shaking or vibrating the filter in view of generally cleaning it through a removal of collected dust and dirt particles, wherein such shaking or vibrating of the filter is brought about by submitting the same filter to stresses induced at a constant frequency.
For the record, following patent publications may be cited in this connection:    JP 2007296050 A2,    JP 2007268120 A2,    JP 2007260037 A2,    US 20070226953 A1,    JP 2007125294 A2,    EP 1776912 A2,    WO 07031497 A1,    JP 2006081634 A2,    GB 2428559 A1.
On the other hand, providing means capable of ensuring a particularly intensive, vigorous shaking action, as obtained with the aid of a motor having a rotor coupled to eccentric masses, which therefore are unbalancing in the dynamical behaviour thereof, clearly clashes with definite mechanical and construction constraints and limitations as far as not only the construction of the vibrating motor, but also the construction of the same filter plate and the related support frame is concerned.
Such constraints and limitations are easily identifiable by all those skilled in the art and, owing also to them not being any relevant matter as far as the present invention is concerned, shall for the sake of brevity not be explained any further.
As far as the use of a variable frequency in connection with an air filter and the cleaning thereof is concerned, known from the disclosure in the U.S. Pat. No. 7,040,039 is a solution aimed at detecting the degree of cleanliness of a filter by simply measuring the resonance eigenfrequency thereof under fully clean conditions, then measuring the resonance frequency thereof also after its use or at particular or pre-established intervals, and finally assessing the difference, i.e. the deviation of the two resonance frequencies from each other; should such deviation turn out as being greater than a pre-determined value, the filter is considered as being sufficiently soiled (the variation in the resonance frequency having of course been brought about by the soil settled onto the filter plate) and, as a result, requiring specific action to be taken in view of removing such soil and restoring filter efficiency.
On the other hand, neither such patent includes any teaching regarding the means for generating and the utilization modes of a shaking action—either at a fixed or a variable frequency—to the purpose of cleaning the filter plate.